The puzzling mass-independent isotopic enrichment in ozone formation contra
sts markedly with the more recently observed large unconventional mass-depe
ndent ratios of the individual ozone formation rate constants in certain sy
stems. An RRKM (Rice, Ramsperger, Kassel, Marcus)-based theory is used to t
reat both effects. Restrictions of symmetry on how energy is shared among t
he rotational/vibrational states of the ozone isotopomer, together with an
analysis of the competition between the transition states of its two exit c
hannels, permit the calculation of isotope effects consistent with a wide a
rray of experimental results.